Hi, welcome to the forum!
Indeed, it would be possible to add a button to the relay node to act as the main switch for the heating system. But regrettably this feature is outside of the objectives of this project and would mean many changes in the way it is conceived. Besides that, having only a switch on the relay node is a very poor feature if you don’t have a way to set the desired temperature.
Sorry for the disappointment,
R. Campos.